(a) (i) Define the term population. (ii) List two biotic and abiotic factors each that affect population growth.
(b) What are the effects of food shortage on a population?
(c) Describe two methods each for:
(i) improving crop yield (ii) preserving and storing food. Explain the principle involved in each of the methods described.
Explanation
(a)(1) Population is defined as the number of a particular species of organisms in a given habitat.
(ii) Biotic factors that affect population growth are:
(1) Animals
(2) Microbes.
(iii) Abiotic factors that affect population growth are:
(1) Rainfall
(2) Wind.
(3) Temperature
(4) Humidity
(5) Soil acidity or alkality
(6) Attitude.
(b) Effects of food shortage on a population are:
(1) Cannibalism — It is the eating of one another in the habitat in order to survive. This reduces population.
(2) Competition — It is the tendency to struggle for the little available food. This is survival of, the fittest.
(3) Loss of weight — There is loss of weight by individuals which brings about low energy out put
(4) Diseases — There is malnutrition due to shortage of food which results in deficiency, diseases and reduction in the resistance of organisms to infection etc.
(5) Death — Organisms may die of starvation due to long period of food shortage.
(6) Famine — Little food is available to go round the population thereby resulting in severe famine.
(c)(i)Methods of improving crop yield:
(1) Use of fertilizer – Fertilizer should be applied before or after planting to increase the fertility of the soil and this will in turn increase yield. During application of fertilizer, you may broadcast, ring or use the side placement or folia method. Example of fertilizer is NPK. Ensure that fertilizer does not come in direct contact with growing crops.
(2) Crop rotation — This is a system of cropping whereby crops are planted on the same piece of land with each crop following the other in a definite sequence during the same farming season. The piece of land may be divided into five plots and different crops planted on these plots every year in a definite order. Ensure that crops of the same family are not allowed to follow each other in the sequence. Deep rooted crops should follow shallow rooted crops and leguminous crops should be planted on the fallow plot in the sequence.
(ii) Methods of preserving and storing food:
(1) Canning — Foods are preserved in cans or sealed containers. Before storage, heat treatment is applied to prevent spoilage.
(2) Refrigeration — Low temperature inhibits the growth and spread of micro organisms.
(3) Drying and salting
(4) Pasteurisation
(5) Additives
(6) Smoking
(7) Irradiation.